There have been many developments in the field of anaerobic treatment of organic solid and liquid waste, including a simple single-tank system requiring 20 to 40 days for the completion of treatment, a double-tank system with higher treatment efficiency, a system using a fixed or fluid filtering bed, a system wherein bacteria accumulate in large quantities in a reaction tank in a granular or integrated solid form, which has drastically increased treatment efficiency, and a system wherein bacteria are allowed to float and multiply so that their fissiparous membranes are utilized. The efficiency of anaerobic treatment has thus increased remarkably.
However, systems of high efficiency are generally limited to treatment of specific organic matter. It is also considered difficult in general to treat organic matter in low content, and in many cases, advanced techniques are required for the adaptation of bacteria to the systems and for their successful operation.